Acoustical systems for air moving devices



United States Patent 3,120,295 2/1964 Lemmerman lnventor Charles Weddell Coward, Jr.

Mount Laurel Township, New Jersey (RD. 1, Box 64, Moorestown, NJ. 08057) Appl. No. 788,225 Filed Dec. 31, 1968 Patented Nov. 17, 1970 ACOUSTICAL SYSTEMS FOR AIR MOVING em ag 3,232,032 2/1966 Pierce l81/50UX 2,674,336 4/1954 Lemmerman l8 l/33(.22) 2,958,387 11/1960 Greff 181/42 3,181,646 5/1965 Edwards 181/42 F ORElGN PATENTS 614,404 12/1948 Great Britain 181/42 926,088 5/1963 Great Britain... l81/33(.4) 984,817 3/1965 Great Britain... 18l/33(.22) 450,063 4/1968 Switzerland l81/33(.22)

Primary Examiner-Robert S. Ward, Jr.

ABSTRACT: This disclosure shows an apparatus for acoustically treating air moving devices to reduce the inherent noise level of the device. The acoustical treatment consists of a multilayer system of various densities of materials. An air moving device so treated is useful in locations where quietness is a major factor.

ACOUSTICAL SYSTEMS FOR-AIR MOVING DEVICES In many buildings the location of air moving equipment near occupied areas is either desirable or an economic or architectural necessity. Two general paths of noise are evident: one is the noisetransmitted up and down the ductwork and the other is the radiated noise from the fan housing created by both the air rushing through the housing and by the turbulence of the air discharging from the fan wheel. To reduce the transmitted noise, sound attenuation is built into the ductwork either by purchasing'an attenuator orby lining the ductwork with absorptive materials. There ispresently no common commercial method of reducing the noise radiated through the casing except by locating the equipment either remotely from the occupied spacesor in special equipment rooms. Prior art, however, discloses several methods of reducing the radiated noise level through fan casings. Two general solutions have been offered, which include using linings or some absorbent material on the inside of the fan casing or enclosing various portions of the wheel or housing with a dense and rigid material which acts as a sound barrier.

The solutions of purchased attenuators or of special equip-' ment rooms quite often alter sizably the architectural requirements of the building and add to the cost of non-productive areas in the buildings. The solutions shown by prior art for radiated noise, while proving of some value in high frequency and reverberation attenuation, are not as useful in the lower sound frequencies, due to the'greater energy levels inherent in the lower frequencies. These lower frequencies and most higher frequencies are transmitted with high efficiency through a rigid and/or dense wall system. Similarly, these frequencies will pass directly through a fibrouslining with no real measurable attenuation.

The present invention, therefore, deals with a unique improvement in acoustical treatment of air moving devices particularly where radiated noise is of concern, whereby the above disadvantages may be overcome.

Another object of the invention is to provide an acoustical system which is relatively inexpensive and which will not add to the architectural requirements of the installation.

A further object of the invention is to provide acoustical shielding which is adaptable to many different types of fans without a major design change and which will not affect the operation or'the efficiency of the fan.

An additional objective is the provision of an acoustical system which will attenuate withequal efficiency the noise created in both the high and low frequency ranges.

These and other objects and advantages of the invention will be apparent upon reference to the following description and claims taken in conjunction with the accompanying drawings illustrating a preferred embodiment of the invention in which:

FIG. 1 is a fragmentary cross-sectional view ofa casing-for fans and the like, illustrating in detail an acoustical system constructed in accordance with the invention;

FIG. 2 is a cross-sectional elevational view of a tubular fan with the acoustical housing of FIG. I applied thereto and shown in section; and

FIG. 3 is a cross-sectional elevational view of a scroll type centrifugal fan with the acoustical housing of FIG. 1 applied thereto.

Referring now to the drawings in detail and more particularly to FIG. I, the acoustical system includes the inner layer 1 which is a perforated metal or plastic sheet. The inner media 2 is a high frequency absorbing-material preferably glass fibers, but may include flexible foamed plastics, open cell sponge rubber and the like. The middle layer 3 is preferably a thinwalled continuous solid sheet of metal but could include continuous lead sheeting or equivalently dense material. The outer media 4 is a low frequency absorbing material which also has good damping properties, such as sponge rubber, cork or its equivalent. The outer structural casing 5 is normally a plastic or the like.

The inner 'media 2 is normally subject to high air velocities and is therefore structurally contained by the inner layer 1 as described previously. In some applications velocities are low enough that the inner layer I may be omittedwithout diminishing the sound attenuation efficiency of the system.

Often the physical size of air moving devices precludes the purchase of one continuous sheet of metal or other material for the solid continuous middle layer 3. In these instances the purchase of several sheets of material in commercially available sizes is contemplated. Installation of these discontinuous sheets would be made with overlapping edges presenting cffectively a solid continuous sheet as the middle layer 3.

Sometimes additional high frequency absorbing material such as glass fibers is provided in the connecting ductwork to the air moving device. In this instance both the inner layer 1 and the inner media 2 may be omitted from the acoustical system.

In the application of the acoustical system to a tubular type fan 8 as illustrated in FIG. 2, it is pointed out that the acoustical system may function as a support for an internally mounted motor or drive system. The supporting system may also be carried to the exterior of the outer structural casing 5 wherein the acoustical system acts as a lining only.

FIG. 3 illustrates the application of the acoustical system to a scroll centrifugal fan wherein the system acts as lining within the outer structural casing 5.

The acoustical operation of this system is initiated by the noise created by the air passing through the fan housing space 7 and by the turbulence of the air discharging from the fan wheel 6 or 9. The sound radiating outward will pass through the perforated inner layer 1 which acts primarily as a boundary for the rest of the acoustical system. The sound would then intimately contact the inner media 2. This inner media 2 will absorb the bulk of the high frequency sound waves as well as significantly damping any reverberated sound within the unit. The lower frequency and higher energy waves passing through the inner media 2 will contact and set the solid continuous middle layer 3 in vibration, but since this surface is continuous, these sound waves will not pass through this middle layer 3. The outer media 4 and the outer structural casing 5 are therefore efficiently shielded from the noise created by the fan wheel 6 and 9 and within the space 7. The solid continuous middle layer 3, then, will resonate due to the induced vibration, but at significantly lower energy levels due to its inertia than the level which originally set it in motion. The resulting vibration of the middle layer 3 is then damped not only by the inner media 2,.but also is damped very efficiently by the outer media 4 which is specifically selected to resonate out of phase with the radiated lower frequency sound waves from the middle layer 3. The outer structural casing 5 contains the previously described items, functions as a final sound barrier and is the outer structural casing of the fan unit.

In FIG. 2, the operation of the acoustical system in a tubular fan is the same as described previously.

In FIG. 3, the operation of the acoustical system in a scroll type centrifugal fan is the same as described previously.

It will be apparent from the foregoing that this acoustical system results in a number of unique advantages over known devices and thereby significantly extends the usefulness of air handlingequipment. Specifically, the selection of the inner and outer media is only dependent on the acoustical reduction required and may be varied to attenuate certain critical frequencies generated by various types of fans. The system can be fabricated and installed with readily available equipment and by acoustically-unskilled labor without diminishing the efficiency of the system. The solid continuous middle layer and both inner and outer media can be selected to meet specific corrosive, high temperature or vapor conditions while retaining high absorptive efficiencies. The entire system is flexible enough to follow any contours required for high fan efficiencies and for heavy duty fan performance. In practice it has been found that this acoustical system increased the outside radius of a tubular fan by approximately one and onequarter inches. In actual tests the acoustical system was equipment rooms. Purchased attenuators normally require an additional four or five feet of space to reduce noise transmitted up or down the ductwork. This acoustical system is not only contained within the length of the fan but will often provide enough attenuation of this transmitted noiseto eliminate the need to purchase attenuators.

It will be apparent that various modifications ofthis system may be made without departing from the scope of this inven tion. For example, various types of materials may be subproviding proper aerodynamic curvatures for the efficient performance of the fan wheel, said housing being constructed as a sound absorbing system and including an inner flexible perforated layer, a porous sound absorbing layer outwardly of said inner layer, a solid continuous flexible middle layer outwardly of said porous sound-absorbing, layer, a layer of sponge-like consistency outwardly of said .solid continuous flexible-middle layer of greater density than said porous sound absorbing layer and an outer solid structural casing, said solid continuous flexible middle layer being positioned and supported only by the adjacent porous sound absorbing and sponge-like layers, whereby said solid continuous flexible mid stituted in a. different order than described previously. Additional modifications may include adding more layers of the acoustical system or varying the covered areas ofthe casing or internal parts. it is also contemplated, in some installations, that heating or cooling coils or other similar items may be included in the acoustical system, thus adapting it to a variety of uses.

lclaim':

A fan comprising a rotating fan wheel and a housing, a portion of said housing extending circumfercntially around and radially outwardly of the fan wheel and said housing tile layer is resiliently separated fromi-both the inner perforated layer and the outer structural casing.

2. ln a fan as described in claim 1 wherein said porous sound absorbing layer is selected from the group consisting of glass fibers, flexible foamed plastics and open ccll sponge rubbers.

3. in a fan as described in claim 1 wherein said solid continuous flexible middle layer is selected from the group consisting of materials of the approximate density of lead including lead sheeting.

4. in a fan as described in claim 1 wherein said layer of sponge-like consistency is selected from a group consisting of materials well-known for their low frequency damping properties including sponge rubber and cork. 

